Studies of chemical metabolism and disposition are designed to provide both applied knowledge in support of chronic toxicity tests conducted by the National Toxicology Program and basic knowledge of those chemical structure and property relationships which determine toxicity. Studies are designed to determine the absorption, tissue distribution, metabolism and clearance of a variety of chemicals. Recent studies of alkyl carbamates in rats and mice have revealed a marked species dependent variation in the rate of metabolism and clearance of these compounds with the mouse having a much greater capacity for clearance than the rat. However, the capacity of both species for clearance is easily saturated and dose dependent kinetics may account for toxicity associated with exposure to these and similar compounds. Studies of a glycol ether, 2-butoxyethanol, have determined that this compound has a unique toxicity to red blood cells causing rapid and massive hemolysis. This toxicity has been determined to be age dependent, increasing dramatically as the age of the exposed animal increases. The causative factor which accounts for the toxicity of 2-butoxyethanol has been determined to be a metabolite, 2-butoxyacetic acid, and toxicity has been modulated by inhibitors of metabolism and clearance. A study of the major acrylate monomer used in the plastics industry, butyl acrylate, has shown that this compound is rapidly and near completely absorbed from the gastrointestinal tract. Most of the dose is metabolized by rapid hydrolysis of the ester linkage and clearance is also rapid with minimal residues remaining in tissues. As part of the work with butyl acrylate a new metabolite not previously identified for this class of chemicals has been isolated and identified.